The present invention relates to a semiconductor device and a method of manufacturing the device, and more particularly to a package of LOC (Lead On Chip) structure which has a limited thickness.
FIG. 1 shows a conventional semiconductor device of LOC structure. The device comprises a semiconductor chip 1, a tape 2 adhered to a major surface of the chip 1, and inner leads 3 mounted on the tape 2. The inner leads 3 are connected by bonding wires 5 to the bonding pads 6 provided on the semiconductor chip 1.
As shown in FIG. 1, a wiring lead 4 is provided under the bonding wires 5, crossing the wires 5. The wiring lead 4 is applied with, for example, the power-supply potential.
Short circuiting between the wiring lead 4 and any bonding wire 5 must be prevented. To this end, the bonding wires 5 need to be arched over the wiring lead 4, with its height part located above the wiring lead 4. The upper surface of the wiring lead 4 is at the same level as that of each inner lead 3. It is therefore required that the highest part of each wire 5 should be at a level higher than in the case where no wiring lead 4 is provided. Furthermore, that part of the resin-molded package for the device, which is provided on the lead frame, must be so thick that the bonding wires 5 may not be exposed at the surface of the package.
FIG. 2 is a cross-sectional view of the semiconductor device, taken along line II--II in FIG. 1. As shown in FIG. 2, the highest part of each bonding wire 5 must be spaced apart by about 50 .mu.m from the wiring lead 4 and from the surface of the package. The bonding wires 5 would otherwise contact the wiring lead 4 and be exposed.
When the bonding wires 5 are applied to the semiconductor chip 1, the height tolerance for the wires 5 is about 1 .sigma. (=10 .mu.m). The highest part of each bonding wire 5 is likely to move vertically for 4 .sigma., or .+-.40 .mu.m. In view of this, a resin layer which is 180 .mu.m or more thick must be provided on the wiring lead 4.
Generally, the standard thickness for the resin layer on the lead frame is about 0.5 mm in the case of an SOJ (Small Outline J-leaded) package, and is about 200 .mu.m in the case of a TSOP (Thin Small Outline Package). In a TSOP it would be difficult for the resin layer on the lead frame to have a thickness less than the standard value (about 200 .mu.m).